Did anyone else notice John Iovine's article "How to Make Bi-Directional Flex Sensors" in the June issue of Nuts & Volts magazine?
While resistive flex sensors have been available for several years, they haven't been cheap, and the shape options have been a bit limited. Mr. Iovine's article suggests that these could be home-built, shaped-to-order, and inexpensive enough that that many of these could be added to a robot without blowing a hobbyist's budget.
The sensor design seemed simple enough: a sandwich made up of a strip of thin and flexible plastic (stiffener), two strips of thin copper surrounding a resistive layer of some sort, and shrink-wrap tubing to keep the ham and cheese... er, "conductive layers" from squishing out. The resistive layer might be tricky (_cloth_??), but I was fairly sure I had some black conductive bags around here "somewhere" (translation: only a day or two of digging ).
And it looks like Mr. Iovine's approach would make it possible to design (say) a flex sensor that could report, with reasonable accuracy, human finger flexing by using a "club sandwich" flex/copper/resistance design:
flex: ============================== Cu1: ---------- Res1: oooooooooo Cu2: -------------------- Res2: oooooooooo Cu3: -------------------- Res3: oooooooooo Cu4: ----------
Layer Cu3 might look like this from above (not to scale) if you wanted all terminals to be at one end of the sensor:
-----------------------------------+
----------------+R2R2R2R2 | |R2R2R2R2 | |R2R2R2R2 | |R2R2R2R2 | |R2R2R2R2 | |R2R2R2R2 | +------------------+
So I went exploring Saturday afternoon. It looks like I need a new set of places to look for oddments: the two big local art/craft stores (Micheals, Ben Franklin) could provide sheet copper for "embossing", but two thicknesses of their 36ga stuff seemed a bit stiff for small robot sensors. No luck on flexible plastic.
Home Depot had some rolls of copper sheet ("roof flashing") that seemed a bit thinner, but I didn't need 12"x20' of it, not at $33/roll. No plastic there, either. Fortunately we have one "real" hardware store here in Richmond -- Pleasants -- but I foolishly didn't start with them, and now I'm temporarily sidetracked.
The article mentions that parts and pre-built sensors can be ordered from the Images Scientific Instruments 'web site:
Images Scientific Instruments
Has anyone else tried making one of these? If so, what did you use, and what were your results?
Frank McKenney
-- The vice of the modern notion of mental progress is that it is always concerned with the breaking of bonds, the effacing of boundaries, the casting away of dogmas. But if there is such a thing as mental growth, it must mean the growth into more and more definite dogmas. The human brain is a machine for coming to conclusions; if it cannot come to conclusions it is rusty. -- G.K. Chesterton: Concluding Remarks on the Importance of Orthodoxy (1905)
-- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all)